Control system



April 29, 1952 A. J. HORNFECK ET AL CONTROL SYSTEM 5 Sheets-Sheet l Filed Oct. 8, 1948 INVENTORS ANTHONY J. HORNFECK AND HOWARD T. HOFFMAN (E Afro EY April 29, 1952 Filed Oct. 8. 1948 PLATE VOLTAGE TUBE CURRENTS AT BALANCE SMALL UNBALANCE IA IB SMALL NET POSITIVE TORQUE A. J. HoRNFEcK ET AL 2,594,436

CONTROL SYSTEM 5 Sheets-Sheet 2 MODERATE UNBALANCE "B" ooNDucTs EVERY OTHER CYCLE lr" lr." A l B ,l

l l Il l' l l l l l l 1 `l A B A B A B A B Al Bl A2 52:0 A

A B =O A eg A V egB C5) INVENTORS AND ANTHONY J. HORNFECK BY HOWARD T. HOFFMAN April 29, 1952 A. J. HQRNFECK ETAL 2,594,436

CONTROL SYSTEM Filed Oct. 8. 1948 5 Sheets-Sheet 3 MMM AMPLIFIER IO MOTOR l CONTROL FIG. 4

IIOV. A.C

AMPLIFIER IO FIG. 7

M L O Dn T N O C Dn O TI O M AMPLIFIER Q MOTOR OON'TROLII l FIG. 8 L

A. J. HoRNFl-:CK Erm.. 2,594,436

CONTROL SYSTEM 5 Sheets-Sheet 4 m .mi

INVENTORS ANTHONY J. HORNFECK HOWARD T. HOFFMAN Apnl 29, 1952 Filed Oct. 8, 1948 April 29, 1952 A. .1. HoRNr-'ECK Erm. 2,594,435

CONTROL SYSTEM Filed oct. 8, 1948 5 sheets-sheet 5 MOTOR CONTROL II AMPLIFIER AMPLIFIER 6 I INVENTURS ANDANTH'ONY J. HORNFEGK HOWARD T, HOFFMAN @wia/TW- Patented Apr. 29, 1952 CONTROL SYSTEM Anthony J. Hornfeck, Lyndhurst, and Howard T. Hoffman, Cleveland, Ohio, assignors to Bailey Meter Company, a corporation of Delaware Application October 8, 1948, Serial No. 53,448

Our invention relates to a system for measuring and/or controlling the magnitude of a variable such as temperature, pressure, rate of fluid flow, position, or displacement, although the variable may be of any chemical, physical, electrical, thermal or other characteristic.

In accordance with our invention Variations in a variable quantity, quality or condition are translated in'to variations in an `electrical effect and this ei'ect is then amplified solely through electrical or electronic means until suflicient power is available for doing useful work such as moving an indicator or other exhibiting means or for regulating the rate of application of an agent contributing to the production or maintenance of the variable.

. In systems of the same general type at present known wherein variations in the variable are translated into variations in an electrical elect the necessary amplification is `done at least in part by mechanical means. There are therefore variations in the magnitude of the variable translated into variations in an electrical eiiec-t which is then translated into a corresponding mechanical movement such as the deflection of a galvanometer and thence usually the mechanical movement is translated vback toan electrical effect for operating the exhibiting or control device. Because of the small 4power available in the rst electrical effect this device is usually operated on a periodic or step by step principle. That is to say upon a change in the variable the exhibiting or control device is not continuously operated in correspondence with such change or changes but periodically by means of a feeler mechanism an exhibiting or control device is changed an amount corresponding to the amount of change -in the variable during succeeding increments of time. Such step by step and ieeler mechanisms are well known in the art.

It is evident that such devices are necessarily complicated and delicate and do not correctly exhibit the variable during transient periods. Our invention is particularly concerned with the elimination of all mechanical movements between -the sensitive device and the exhibiting or controlling device, leading to simplication and removal of the usual time delay, so that the device accurately exhibits the magnitude of the variable even during transient periods. It is evident that many ancillary advantages will follow, among which may be mentioned as obvious the elimination of wear of mechanical parts and the elimination of the necessity of .periodic inspection and adjustments to correct for inaccuracies occasioned by mechanical wear.

The great majority of low level D.C. measuring systems such as thermocouple-potentiometer recorders use a galvanometer for detecting or measuring the D.C. input signals. The gal- 17 Claims. (Cl. 318-28) vanometer is a relatively fragile device and is affected by mechanical vibration and is easily damaged by overload. Vacuum tube or electronic amplifiers for low D.C. voltages have not been successful because of instability in tubes. A particular object of the present invention is to provide apparatus and a new method of detecting and amplifying small D.C. voltages or current.

Systems have been devised for measuring small A.C. signals utilizing the Wheatstone bridge and other types of electrical networks with phase sensitive amplifiers.

In measuring circuits of relatively small A.C. or D.C. signals representative of the variable quantity, quality or position to be measured it is usual to desire the indicating pointer, the recording pen, or the control pilot valve to be positioned by a reversing pilot motor. The requirements of the system is then to have a motor control circuit sensitive to the electrical signal which is representative of the variable or change in value of the variable. Such motor control circuit must include the necessary system and apparatus, sensitive to phase or polarity of the signal and for amplifying `the same to selectively cause motor rotation in desired direction and degree depending upon the value of the variable or the `departure of the variable from some predetermined or previous value.

A principal object of our present invention is to provide an electrical and electronic motor control circuit universal in nature in that the electrical sensing and amplifying network preceding the motor is without change sensitive to phase and magnitude of an A.-C.signal or to polarity and magnitude of a D.C. signal.

Another object is to provide an electrical and electronic measuring system of motor control having an electronic inverter which is a phase discriminating amplifier receiving a small A.C. signal and producing an amplified D.C. output for motor control. In certain preferred embodiments of our invention we utilize a device which we term a reactor-converter which converts the D.C. signal of varying potential into a greatly amplified A.C. signal of reversible phase. If the D.C. signal reverses in polarity a consequent reversal of phase is effected in the A.C. signal. The apparatus includes a pair of iron core reactors and has all of the sensitivity of the galvanometer as well as the s'turdiness of a transformer. There are no delicate moving mechanical parts to wear out or become damaged.

The reactor converter produces a greatly amplied A.C. output signal of reversing phase which is supplied to a phase sensitive electronic amplifier and motor control circuit. In this way a thermocouple having an output of only a few millivolts is used to position a reversing motor with no intermediate mechanical or moving 3 parts. The reversing motor may then position an indicator or recorder and at the same time a potentiometer for balancing the system which may be of the null type.

A particular object of our present invention lies in the amplifying and motor control circuit arrangement whereby increased sensitivity as Well as an increased speed of rebalancing is accomplished without undue overtravel or huntfing which in the past has almost invariably ac- .'tion of Fig. 1.

."Fig. 4 is a simplified wiring diagram, based on Fig. 1 wherein thesignal is a low level alternating current of reversible phase.

Fig. 5 is a schematic wiring diagram of a measuring circuit responsive to the A.C. un-

, balance of a Wheatstone bridge utilized in tem-vr perature measurement.

Fig. 6 is a circuit somewhat similar to Fig. 5 but utilizing a thermocouple in temperature measurement.

Fig. 7 is a schematic wiring diagram of a tele- A` metering circuit.

Fig. 8 is a schematic wiring diagram of another form of telemetering circuit.

Referring now specifically to ligl'we show therein a complete wiring diagram for the measurement of speed of a tachometer generator as representative of speed of any rotating object f which may be adapted to drive the tachometer generator. The principal components of the circuit include an amplifier I El having input terminals I, 2 and output terminals 3, the latter comprising the input terminals of a thyratron motor control unit II having output terminals 5, which comprise the input terminals of a reversing A.C. motor I2 for positioning recording and controlling instrumentalities. A low level D.C. signal of reversible polarity is impressed upon thegterminals i, 2 and the arrangement provides at the terminals 5, 6 a pulsating D.C.

i output having a 60 cycle component of reversible phase and variable magnitude when an unbalance signal exists across terminals I, 2 causing the :motor I2 to rotate in desired direction and speed. When no signal appears at I, 2 (bal ance) the 60 cycle component at 5, 6 is reduced to zero and no motor torque results.

In Fig. 1 a tachometer generator i5 is adapted to produce a low level D.C. signal whose value is representative of rotational speed of the tach- ,ometer Vand thereby of whatever equipment is vdriving the tachometer. vpotentiometer circuit including a portion of a We provide a D.C.

resistance I'I which is supplied with regulated direct current from a source I6. An adjustable contactarm I8 is movable over the resistance I1 by the motor I2 for balancing the network.

'Ihe previously mentioned terminals I, 2 are connected in the loop including the elements I5 and kII and when the D.C. voltage generated by the tachometerv I5 is equal to that existing across the included portion of the resistance I1 there will be no voltage impressed across the terminals If, from a condition of-balance, the tachometer speed increases with corresponding increase in D.C. output a voltage will exist across lthe terminals I, 2 of one polarity and of a magnitude depending upon the difference between the D.C. voltage generated by I5 and the D.C. voltage -towhich it is compared. If tachometer speed decreases then the voltage across l, 2 will be of opposite polarity and again of a magnitude dependent upon the extent of unbalance. In general it may be said that the D.C. signal across the terminals I, 2 Will be of a polarity determined by the direction of change of tachometer speed and of a magnitude determined by the extent of Vsuch change. rihe D.C. signal is amplified and utilized tolcontrolV directional speed of the motor I2 to position the arm I8 along the'resistance I'I to bring the D.C. potentiometer loopback into balance under which condition zero signal will exist across the terminals I, 2.

TheV amplifier I is polarity sensitive to the signal at I, 2 for producing at 3, 4 an amplified D.C. voltage of reversible polarity. The device IE) is shownas a-single envelope tube containing triodes 2li and 2|; of which triode ZI is a rectifier supplying a reference voltage E2 which is pulsating direct current resulting from halfwavev rectification of the alternating current supply. The ktube I0 is preferably such as a 6SN7, with grid controlled triodes, having a linear output voltage characteristic about evenly divided across the grid condition of zero impressed voltage. Manually adjustable contact 22 establishes the value of the reference voltage E2 output of'triode 2 I. The value of E2 is established indesired relation to the value which Eli will have under the condition of zero voltage Y across terminals I, 2. In other words, under such condition, E2 maybe equal to E1 or may be biased above or below 'E1 through theagency of adjustable contact.22.

Triode 20 is polarity sensitive as to the voltage across I, 2 for producing a voltage E1 to be compared tov the reference voltageEz. Any voltage at I, 2 isfimpressed between the grid 23 and cathode 25. When the circuit I5, Il, I3 is in balance and no voltage exists across the terminals I,z2 .the Vtriode 2li-will pass pulsating direct current resultingfrom half-wave rectification of .the A.C. supply. In vthe present embodiment we preferably adjust 22 so that E2 is substantially equal to E1 .at a condition of zero voltage across I, 2. Thisiis the condition of greatest stability and allows approximately equal regulation in either direction from a zero voltage output across terminals 3, II.

When the tachometer speed increases or decreases and the D.C. potentiometer circuit becomes unbalanced a, low level D.C. voltage appears at I, 2 and is applied to grid 23 of triode 2G. If, forl example, .the tachometer speed has increased and a positive voltage appears at terminal I and grid 23 then there is an increase in plate current and an increase in voltage E1. The difference in voltages'Er-'Eh appears at terminals 3,4 as a pulsating D.C. Voltage of one polarity and of a value determined by the extent of circuit unbalance.

Whenthe tachometer speed decreases a voltage appears at terminals I, 2 of which terminal 2 is positiveand theplate current of triode 20 is decreased as is voltage E1. The difference in voltages Ez-El appears at 3, 4 as a D.C. voltage of opposite polarity and of a value determined by the extent of unbalance as shown by the magnitude of the signal across I, 2.

Thus the amplifier I receives a low level D.C. signal of reversible polarity determined by the direction of unbalance of the D.C. loop I5, I8, I'I and of a magnitude determined by the extent of such unbalance. The amplifier I0 is polarity sensitive and produces at terminals 3, 4 an amplified D.C. voltage of polarity determined by polarity across I, 2 and of a value varying relative to a reference value in accordance with magnitude of the signal at I, 2.

The output at 3, 4, while of amplied voltage .is at a relatively low current value, as supplied to the control grids of thyratrons A and B of the motor control circuit I I. With zero D.C. signal across terminals 3, 4 the thyratrons A, B will have equal output of alternate half-waves and no rotation of the motor I2 will result. Rotation of the motor I2 occurs only when the power output of thyratrons A and B is unbalanced with the direction of power unbalance determining the direction of motor rotation.

.The motor control circuit II includes two thyratron tubes A, B having their anodes energized by a split secondary winding of a transformer 35 and their cathodes connected through an adjustable resistance 21 and a condenser 23 arranged in parallel and through a motor winding 29 to the mid-tap on the transformer secondary. Equal resistors IGI and 03 complete the grid-cathode circuit of each thyratron by connecting their individual grids to the common cathode connection. The two circuits so completed by the resistors are then, as a unit, discriminatory between polarities of the input signal to terminals 3 and 4. Filtering capacitors IDI) and |02 are placed in parallel with each of the resistors to smooth out the pulsations of the D.C. voltage applied to the thyratron circuits. Another winding 30 of the motor I2 is energized directly from an A.-C. source. We term the elements 21, 28 a cathode bias and in Fig. 3 we show a rearrangement of certain portions of the circuit of Fig. 1 for ready study in connection with the graphs of Fig. 2.

AOne of the thyratrons A or B is conductive during a half cycle when the output of the amplifier I0 at terminals 3, 4 is of one polarity and the other thyratron is conductive during a half cycle when the polarity at terminals 3, 4 is reversed; while at balance (with zero D.C. signal across 3, 4) both thyratrons are ring over a portion of the positive half cycle of plate voltage (see graph 2, Fig. 2).

The connection of the resistance 21 and the capacitance 28 in parallel, in the output circuit y of the thyratrons adjustably biases the grids and the resistance 2I and we term this a sensitivity adjustment. The bias can be adjusted so that ferent conditions.

Graph 2 represents thyratron effect upon winding 29 for a condition of balance at terminals I, 2 with a recurring pattern for each tube over three or four cycles and a net balance upon the motor winding resulting in no rotation.

Graphs 3, 4 and "5 represent thyratron output for various conditions of unbalance in one direction and signals of corresponding magnitude at terminals 3, 4 of one polarity. Similar graphs may be made for conditions resulting in motor rotation in opposite direction.

An unbalance of the measuring circuit will produce a grid signal on one thyratron to oppose the bias and on the other thyratron to aid the bias. A small signal will increase the average current conducted by one tube byv increasing the period of conduction, and it will reduce the average current conducted by the other tube by reducing the period of conduction. (Graph 3.) Upon change in signal value the shaded areas will shift and in about three or four cycles will settle down to a relative value representative of the signal. The net algebraic summation of the shaded areas determines the speed of motor rotation. Graphs 3, 4 and 5 are all on the basis of tube A predominating and the same direction of rotation.

Graph Ll depicts a moderate unbalance with the average current passed by each thyratron modulated differentially from zero to maximum. Tube B conducts only every other cycle.

A large unbalanced signal (Graph 5) will cause one tube to re over entire half cycle and completely extinguish the other tube. As the signal value increases, tube B conducts over fewer and fewer half cycles until finally the signal value increases to a magnitude where tube B is completely extinguished.

Motor torque is the result of the diilerence between the power output of the thyratrons A and B. At balance the outputs cancel out. For unbalance the direction of motor rotation is determined by whether the output of A or B isthe greater and the speed of motor rotation is determined by the difference in thyratron output. For small signals of one polarity the output of A (for example) increases while that of B decreases and for larger signals of the same polarity B may actually decrease to zero while the reverse is true on the opposite polarity.

The modulation of the tube currents to obtain smooth control on the reversing motor is obtained by the design of the cathode bias circuit including elements 27 and 28. When zero voltage exists across terminals 3, 4 the output at terminals 5, B balances and the motor does not rotate. When an amplied D. C. voltage of one polarity exists across terminals 3, 4 then thyratron A (for example) will conduct in excess over thyratron B. The graphs of Fig. 2 illustrate, with reference to thyratrons A, B, the nature of the output across terminals 5, 6 in relation to the magnitude fthyratrons.

of the'sgnal existing across terminals I, 2. The

result is to selectivelyfsupplya'pulsating direct current having a 60 cycle component of reversible phase and variable'magnitude to Vmotorl winding 29. The phase of this A. C. componentand consequently thefdirection of -motor rotation isdetermined by which tube predominates in its conduction. The vmotor winding is tuned by means of the parallel capacitor 3 I.

By means of the cathodebias 27, '28- on the thyratrons it` is possible to obtainmodulating control lfrom a variable magnitude rather than variable phase grid Voltage. The peculiar anticipatory action of the bias together with thel dampv ing eifect'of' the relatively largeD. C. motor winding current when both tubes conduct makes the system nearly'dead-beat lwith .1% sensitivity.

Furthermore, -motor reversal is accomplished withv grid, signals was' low as lilmillivolts Von the There is'of course Athe possibility of operating the thyratron motor control I I directly f from Yameasuring signal Vwithout additional 'amplifiers in cases Ywhere 'the available signal power is fairly large and isapplieddirectly at the -terminals 3; 4.

The motor I2 is an induction Imotor having a -two-pha'se'stator .winding anda high resistance squirrel cage type rotor. There are two identical The capacitor 32 is quency and forms a `series resonant circuit. This yresults in Va voltage across the winding 3B Awhich isapproximately double the line voltage for the particular motor used.

The second winding 29,- which we term the control winding, 'while identical with the rst winding'30 in construction differs in that itY has a acapacitor 3| connected in parallel across it. The

capacitor SI-is designed to produce a condition of parallel resonance at line frequence. It will 'be understood thatwhile the dra-wing shows a 60 cyclel power'source the line frequency is not so limited to 60 cycles. At balance, some current Aflows through each half cycle of the applied potential across'5, 6.

vIt vwill' be seen-that the amplifier circuit I0 and motor control circuit II are substantially independent of each other to the extent that they lmay be supplied from alternating current sources l of entirely diiferent frequencies if desired. In

other'words'the transformer -35 may be split into two transformersone for the motor control and motor circuit whichmay be commercial 60 cycle frequency while aseparate transformer forthe ampliiier circuit may be of a much higher fre- -quencyiffdesired (see Fig; 6)

In`Fig.-1 the motor I2 is shown as simultaneouslypositioning the balancing contact I8, arrecording pen 36 and a pneumatic pilot valve 33'. -Thepen v36 is positionable relative to a visual lindex 38 and to ya time revoluble chartv 39. Pilot Vvalve 31' may bel of a type described in the pat- -fent to Johnson 2,074,696 whereby an air loading pressure is continually established useful in the rcontrol of the same variable vwhich is responsible Vfor'changes-in the signal across the terminals I; 2 or in the control of another variable or variables which may or may not contribute tothe value of-the signal at terminals I, 2.

"Inl general the operation of the system so far described-provides an indication and continuous record of the value of the variable, in this case speed, and establishes a controlV force representative of such value.

In the particular example described it is desired to continuously ascertain the value of a speed of which the tachometer generator I5 output is representative and to utilize the control force either in the control of such speed or of another variable.

The D.C. potentiometer loop is of the null balance type such that when speed is unchanging, regardless of its value, the potentiometer circuit is balanced and the signal across terminals I, 2 is of zero voltage. Upon change in speedy the loop becomesV unbalanced and a signal at terminals I, 2 provides a D.C. voltage of one polarity or the other determined by the direction of unbalance (direction of speed change) and of a magnitude determined by the extentof such unbalance. The signal is impressed `upon lthe amplier I@ which is polarity sensitive and produces an amplied direct current at the terminals 3, 4 of' polarity determined by the' polarity of the signal and of a magnitudeV determined by the magnitude of the signal. The'motor control circuit I! normally produces a-balanced condition as to the terminals 5, 6 so that the motor I2 does not rotate. If a signal of one polarity or the otherexists across terminals 3, l then one thyratron or the other predominates to selectively control rotation of the motor yI2 in desired direction -whereby the recordingk pen 36 is moved from itsprevious speed Value to the new speed value thus providing a continuous indicaticn and record of the actual speed of the tachometer generator. At the same time' the motor I2 positions the contact I8 along the resistance slidewire l? in proper direction to rebalance the loop and return the signal at terminals I, 2 to a zero value resulting in a cessation of movement of motor I2. In other `words when the position of the pen 35, the pilot 31 and the contact IS are representative of the speed of tachometer i5 the motor I2 is at restand such overall condition persists until a change in tachometer speed occurs.

In Fig. 4 we illustrate an adaptation-of -our invention in the control of direction'and'speed of rotation of the motor I2 responsiveY to'a signal at terminals I, 2 which is of reversible phase alternating current. Thus it will be understood that we have provided a motor control system of universal type, i. e. responsive to either direct current or alternating current without change in its general arrangement. We illustrate herein diagrammatically the amplifier I0 and the motor control circuit I I asbeing the same as those shown and described in detail in Fig. lfeiicept possibly for electrical values of theV component parts.

For establishing a signal at terminals I, 2 we have shown an A.C. telemeter'application of the null balance type. fldindicates theV transmitter of an induction bridge telemeteririg circuit having series connected windings 4I,'42con nected in loop with a divisible sldewire resistance 43 by conductors 44, 45. The'loop 4l, 42, 45, 43 and 44 is energized from an alternating'current transformer 43. Positionable within the 'windings 4I, 12 is a magnetic core piece 41 which may have a float or forcevmovable member 48, 'the whole Vcomprising a transmitter of the rotameter type. Such a meter is used in measuring the rate of flow of auid and variations in rate of flow cause a positioning of the elements 48, 41 to the end that the location of core 4IV relative-to the windings 4|, 42 is continually representative of iiuid rate of flow which is to be measured.

Positionable along the slidewire 43, through the agency of the motor l2, is a contact arm 49. The motor |2 may cf course simultaneously position an indicating and recording pen and control instrumentality such as described in connection with Fig. 1.

A conductor 59 joins the movable contactl arm 49 with a mid-tap of the windings 4|, 42 to the end that the conductor 50 is susceptible to unbalance of the loop. When the system is in balance and the circuit 4|, 44, 43, 49 and 59 has the same voltage condition as the circuit 42, 45, 43, 49 and 50 then no voltage exists across the terminals 2. Under this balance condition the motor |2 is stationary andthe slidewire 43 is then divided by the arm 49 in proper proportion, relative to the voltages and windings 4|, 42, so that the two loops are in balance.

If iiuid rate of flow increases (for example) and the elements 48, 4`| move upwardly then the Voltage in windings 4|, 42 become unbalanced and a voltage of one phase appears across terminals 2 with the result that motor |2 is energized for rotation in proper direction to position the contact arm 49 along the resistance 43 in a direction to rebalance the circuit. As soon as balance is attained through positioning of the arm 49 the signal at l, 2 reduces to zero and the motor 2 stops. Thus any departure from balance of the measuring network results in an A.C. signal across terminals I, 2 of phase determined by the direction of unbalance and of a magnitude determined by the extent of unbalance. Such unbalance results in operation of the system and motor 2 to correct the unbalanced condition :and return the system to balance.

It is believed unnecessary to go into greater detail as to the operation of circuits I9 and upon occurrence of an A.C. signal at terminals 2 for the operation is substantially identical with that described in connection with Fig. l. The triode 20 is responsive to either change in polarity or change in phase of a signal at terminals 2. If the signal of Fig. 3 is of one phase it will be in phase with the plate current of triode 2) and tend to increase the voltage E1. If the A.-C. signal at terminals 2 is of opposite phase it will be out of phase with the plate current of triode 20 and tend to reduce the value of voltage E1. Thus our improved motor control circuit comprising the elements and is equally as responsive to a D.-C. signal or to an A.C. signal due to the triode 20 being either potential responsive or phase responsive.

We have found that this system is particularly' satisfactory for A.C. telemetering applications where the A.C. circuit has a very poor null balance characteristic. The unit has the peculiar ability to select a 60 cycle iii-phase component of the input signal and reject harmonics and outof-phase unbalance which have a paralyzing effeet on some types of ampliers.

In Fig. we illustrate the adaptation of cur invention to a temperature measuring system wherein the signal across 2 originates with an A.C. resistance thermometer bridge circuit having a very low A.-C. signal resulting from a very low temperature span. 5| is a phase sensitive alternating current bridge having fixed resistor arms 52, 53 and 54. The fourth arm 55 of the bridge 5| is a resistance' element located at any desired 'location where temperature is to be measured. For balancing-the network-we' provide- 10 an adjustable resistance 56 inserted between the arms 53 and 54 and provided with a movable contact arm 5l for proportioning the resistance 56 between the arms 53 and 54. The bridge 5| is supplied with alternating current through a transformer 53.

The motor l2 is adapted to position the arm 51 as well as the recording pen 36 to provide an indication of temperature as well as a continuous record of the value of temperature to which the resistance arm 55 is sensitive.

Preferably the bridge arm 55 is a platinum resistance measuring element and in the particular application is to be sensitive to a very 10W temperature span resulting in a very low A.-C. signal at terminals 59 and 60. For an understanding of a phase sensitive alternating current bridge for measuring the resistance of the leg 55 subjected to temperature to be measured reference may be had to the Ryder Patents 2,275,317 and 2,333,393. The conjugate voltage supplied to the terminals 59, B0 as an input to an ampliiier 6| assumes a balance or unbalance and a phase relation relative to the supply voltage dependent upon the magnitude and sense of the unbalanced condition of the bridge 5|. The amplifier 6| selectively provides an amplied A.-C. signal to the terminals 2 and, as previously explained, the discriminator amplifier l0 is phase sensitive to the signal appearing at terminals I, 2.

In general the system of Fig. 5 provides for the accurate measurement or" extremely low temperature spans to which the resistance arm 55 maybe subjected. The minute A.-C. signal of reversible phase appearing at terminals 59, 69 is amplied to produce at terminals 2 an A.C. signal of reversible phase of considerably greater value than that at terminals 59, 89 and of a phase determined by either increase or decrease in temperature at 55 and of a magnitude determined by the extent of change in temperature. The signal appearing at terminals i, 2 results in a rotation of motor l2 in proper direction and amount to move the arm 51 over the slidewire 56 and rebalance the A.C. network 5|.

In Fig. 6 we illustrate the adaptation of our improved motor control circuit, in the measurement of temperature utilizing a thermocouple, for detecting small D.-C. voltages or currents. The present embodiment involves the use of a device (which we term a reactor converter) which converts the low D.-C. signal of reversing polarity into an amplified A.-C. signal of reversing phase. It includes a pair of iron core reactors and has all the sensitivity of a galvanometer as well as the sturdiness of a transformer. There are no delicate moving mechanical parts to Wear out or to be damaged. Reference may be had to the application of Anthony J. Hornfeck, Serial No. 506,632, led October 18, 1943, now Patent No. 2,494,876 granted January 17, 1950.

The reactor converter produces an amplied A.-C. output signal of reversing phase which is supplied to a phase sensitive electronic ampliiierof the type mentioned at 5| in Fig. 5 for supplying to the terminals i, 2 and A.C. signal of reversible phase. In this way a thermocouple having an output of only a few millivolts D.-C. may be utilized to control the reversing motor |2.

A thermocouple 'lil is sensitive to the temperature to be measured and is connected in a potentiometer system including the balancing potentiometer 7| having a movable contact arm 'I2 positionable by the motor l2. Unbalance signal ofthe potentiometer including elements l0,

and I2 .is fed to Vwindings 13,' 'I4 of reactorsi'ISj'ISff inla bridge circuit-.11. The output oflthe vbridge 'I'I vappearsacross terminals v59, 601as-'an"A.-Cf.' voltage of. reversible phase determined by fltlie sense 'of unbalance of the potentiometer .circuiti and of a magnitude determined by 'the-extentotI unbalance. In general the action of the reactor converter is one of changingfa`D.-C. 'signal-ofi given polarity `into a greatly amplified A.C..' signal of given phase and the .ability"Orrevers` ing the phase of the alternating currentsignal.: 180 when the polarity or sign of thedi'rectcurrent signal-is reversed.` We have mentioned "the amplifier BI in connection with Fig. 4 -andzsuch' amplier vmay not be required between'the'termie nals `591,' SII and the terminals 1|,2 at the input'of the amplifierv |and the motorcontrol kI I. Irif general the arrangement of Fig. 6 Villustrates'a thermocouple 'I0 producing low level DAC. signals:

of reversing polarity and of `varyingmagnitude"20-=' dependent upon direction and 'extent of' change of temperature to which the thermocouple .'10 is sensitive' from any previousk temperature;

Such change results Ain an unbalance of 'the'potentiometer loop andthe low level D.C*. voltage' of reversing polarity is, through the `agency-*of I circuits 'I'I and 6| impressed' at terminals "I, A2 l as an amplified A.C. signal of reversing phase which through the agency ofthe amplifierII) and the motor control circuit 'I I results in a rotationf of motor I2 in properV direction and extent -to cause thecontactV 'I2 to move-over the slidewireV 1 'II and rehalance` the potentiometer circuit;

Speed control of the motor I2 is dependentV upon magnitude of the signal reaching the'term'inals I, 2 and therefore determined by lthe lextent `or unbalance of the system 'IIL-1|',` '|2.

pose two slidewire resistances '19and-80.' IiromV the input terminal 4 we join'a conductor 8| with Y a contact arm 82 adjustable over the resistance 80 and from the terminal 3 join a'conductor4 83, through a xed resistance 84 tol-a terminal -85 which is thev junction between 4resistance V19 and 80. The circuit 4, 8|, 82,I 80, 85, 84, 83- pro"` vides a feed-back ofA direct current lfrom the c output 3, 4 of the amplier I0 to the inputofnet-Y Work 'II and such feed-back isv thereforepropor tional to the. magnitude of the unbalanceasrepresented at terminals 3, 4.

Also connected across the outputterminals'.

3, 4 is a second feed-back whichmay abe traced' ,551,

from terminal 4 vthrough conductor 8|, con-- ductor 86, contact 81, slidewire 'IIL-resistor 88,- i resistor 89,l capacitor 90 and conductor 83 `to terminal 3. This arrangement provides a sepan-v ate feed-back proportional to the rate of'change of the signal at terminals'S, 4.

The two feed-backs serve to minimize overtravel and hunting of the motor by modiying the demand for motor .rotation .originating with'` change intemperature to which the therrno couple .I0 is sensitive.

In Figi? we show the amplifier I0 andmotor control II sensitive to unbalance of `a telemetering system `having Va transmitter Tand are-I ceiver R which may be adjacent or spaced a considerable distance apart.Y The transmitter andreceiver each comprise a movable core trans-.- formerincluded in a balancable loop'circuit..l

The transmitter T includes. an alternating-cura;

rent energized .primary ,windingH I I0: `and-a pair/75 reaction-representative of.v the value of said vari-,ff

of 'opposed-.secondary-windings III and H2. A

movablei core"f:|I3-Smay be positioned by any variable whose yvalue .is to be remotely indicated.

" Thereceiver iis.' similarlyprovide'd with an energized'primaryI I4 anda pair of opposed second.-

ariesiI |5,.I I6 coupled by movable core I I'I. The

secondaryrwindings III, II2, |I and .IIS areconnected in a series loop across terminals I, 2

ofthe motor control. The loop circuit receives Lcurrent inductively from the primaries III),v IIf'l vl-tioned in either direction from a central locationfthrough the agency of a ow meter, Bourdon tube'or.r similar device.v In its neutral position the'secondaries I||,V I|2 receive equal energization inductively from .thel primary lI IIJ and cancel out. Movement ofthe core inone direction produces la'voltage in winding I I I greater than that in I I2 and viceversa.` Similarly movement of the-core AI I'I causes an unbalance of voltage between :the windings'l I5 and IIS.

From a condition of balance, with no voltage signal'across the terminals I, 2, a change in position of th'e variable actuated core II3 produces v aty the terminals I, 2 a signal in direction and magnitude dependent upon the direction and extentof lmovement of the core IIS. Such unbalance signal at the terminals I, 2 results (as previ-` ously explained) in a rotation of the motor I2 in proper direction and extent to position the core I I'I insuch a direction as to balance the loop including thel windings III, II2, H5 and |I6 and return the unbalance signal across the terminals |,'2 to zero value.

In somewhat similar fashion We show in Fig. 8 a telemetering circuit having a transmitter `T including* an energized primary winding IIS' coupled to a pair of secondary windings IIS, by means of a positionable core piece I2 I'. Atv the receiver R we show a slidewire |22 having a movable contact armI 23 and connected in series 5g-.circuit with fixed resistances' |24, |25 and primaries ||9, |20. A conjugate conductor |25 joins the contact arm |23 with a mid-tap of thesecondaries ||9, |20. The contact arm |23 is arranged to be positioned along the slidewire |22 through the agency of the motor I2.

When the system is in balance no signal appears across the terminals I, 2. If the transmit-Y ter core |2| is'moved from its previous position an .unbalance of induced voltage exists in the @windings IIB, |20 producing a signal across `the AV"scribe certain preferred embodiments of our invention it will be understood that this is by way of example only and is not to be considered as limiting. i

What we claim as'new'and desire to secure by Letters Patent of the United States, is:

1. A system for measuring the value of a vari# abieAc-omprising in combination, means actuated by said variable for establishing-.an electricalv signalVV changeable in Vmagnitude and relativediable, a thermionic tube having an anode, cathode and grid, an impedance, a source of alternating current energizing a circuit comprising said anode, cathode and impedance, means applying said signal to the said grid-cathode to control the potential across said impedance, a source of potential on the order of that in said impedance, means to adjust said second potential to a desired value of that in the impedance when the said signal is zero, an output circuit combining said potentials in opposition to produce a D.C. potential of reversing polarity, a pair of thyratrons having their anodes energized from opposite ends of a centertapped secondary, a two-phase motor having a winding energized by alternating current and a second winding connected between the center tap and the cathodes of said thyratrons, a cathode resistor biasing said thyratrons to an intermediate output at zero control potential, means connecting the terminals of said output circuit respectively to the grids of said thyratrons to control the preponderance of output thereof, and an indicator actuated by said motor for movement over a scale.

2. The system dened in claim l in which the motor and thyratron output circuits are energized at a commercial frequency and the other circuits at a higher frequency.

3. A system for measuring a variable comprising in combination, means responsive to said variable to establish an electrical signal of magnitude and relative direction representative of the value of said variable, a thermionic tube having an anode, cathode and grid, an impedance, a source of alternating current energizing a circuit comprising said anode, cathode and impedance, means biasing said grid for anode current of substantially one-half maximum, means applying said signal to the said grid-cathode to change the potential across said impedance resulting from said one-half maximum current, a potential adjusted to a desired portion of the value of that in said impedance when the said signal is zero, an output circuit combining said potentials in opposition to produce an amplified D.-C. potential of reversible polarity, a pair of power tubes, a center-tapped secondary oppositely energizing the anodes of said power tubes, a two-phase motor having a winding energized by the same source as said secondary and a second winding connected between the center tap and the joined cathodes of said power tubes, means biasing said power tubes for substantially one-half maximum output, means connecting the terminals of said output circuit respectively to the grids of said power tubes to selectively regulate the output of each whereby the direction and speed of rotation of said motor is regulated, and variable-value designating means actuated by said motor.

4. A motor control system comprising in combination, a variable speed reversible motor having two windings, a pair of thyratrons having output circuits including anode and cathode elements, one set of like elements being connected together, a common source of alternating current for one of said windings and said thyratrons, cathode resistor means biasing the grids so that both thyratrons have some conductivity at zero control voltage for the grids, means so associating the output circuits, windings and source that the said thyratrons are energized at opposite.

polarities and one set of like elements are fed through the other motor winding whereby the direction of motor rotation dependsv on which thyratron has preponderant conductivity; a source of reversible direct current of varying magnitude associated with said grids to apply opposite potentials thereto and comprising a thermionic tube having an anode, cathode and grid, an impedance, a source of current energizing a circuit comprising said anode, cathode and impedance, means biasing said grid for substantially one-half maximum anode current, a potential adjusted substantially to the value of that in said impedance at zero grid control potential, an output circuit combining said potentials in opposition for application to the thyratron grids; and a source of grid potential for said tube variable in direction and magnitude whereby the value of potential in Said impedance may be varied in each direction from that of the adjusted potential.

5. The system as dened in claim 4 in which the grid potential for said tube is provided by a tachometer generator and opposing potentiometer and in which said motor adjusts said potentiometer to balance the system.

6. The system as dened in claim 4 in which the said anode, cathode, impedance circuit is energized from a source of alternating current, said grid potential being of reversible phase resulting from a bridge circuit comprising a solenoid and a resistor parallel connected and energized from said A.-C. source, a slider on said resistor mechanically connected to be actuated by said motor, a midtap on said solenoid, said grid potential being taken from the slider and midtap, and a core movable in said solenoid and adapted to be positioned by a variable to one or the other side of the center thereof.

7. The system as dened in claim 4 in which the said anode, cathode, impedance circuit is energized from a source of alternating current, said grid potential being of reversible phase resulting from a resistance thermometer, a bridge energized from the same source of alternating current and including a thermometric resistance, a balancing resistor for said bridge having a slider, one conjugate conductor of said bridge being connected to said slider and an opposite point in the bridge to produce an A.C. output of reversing phase and variable magnitude, said motor being mechanically connected to said slider to balance the bridge, and an amplifier energized by direct current adapted to amplify the said A.-C. output and apply it to the grid of said tube.

8, The system as dened in claim 4 in which the said anode, cathode, impedance circuit is energized from a source of alternating current, said grid potential being of reversible phase resulting from a reactor-converter comprising a pair of saturable core reactors each having an A.C. winding and a pair of impedances forming a bridge having one conjugate energized from said source and the remaining conjugate supplying said grid potential, each reactor having a bias winding and a signal winding, a source of direct current energizing said bias windings and a D.-C. signal of reversible polarity so supplied to the signal windings as to oppose the bia-s of one reactor and aid that of the other dependent on the direction of thesignal voltage.

9. The system as defined in claim 8 in which the source of the D.C. signal of reversible polarity comprises a thermocouple and a battery energized potentiometer arranged in opposition, a slider on said potentiometer and a mechanical connection ybetween the motor and slider to balancethe circuit.

10. The system as defined in claim 8 in which the source of the D.-C. signal of reversible polarity comprises a thermocouple and a battery energized potentiometer arranged in opposition, a circuit delivering the unbalance voltage of said potentiometer and thermocouple to said signal winding, a network associated with said last mention circuit and means conductively associating said network and the reversible D.-C. potential applied to the thyratron grids so arranged as to provide a reverse feedback to the signal windings on said saturable core reactors.

11. The system as dened in claim 8 in which the source of the D.C. signal of reversible polarity comprises a thermocouple and a battery energized potentiometer arranged in opposition,

a circuit delivering the unbalance voltage of said potentiometer and thermocouple to said signal winding, a network associated with said last mentioned circuit, means conductively associating said network and the reversible D.C. potential applied to the thyratron grids so arranged as to provide la reverse feedback to the signal windings on said saturable core reactors so as to prevent overtravel and hunting of said motor, a slider on said potentiometer, a mechanical connection between said motor and slider to balance the system and anV indicator actuatediby said motor for movement over a temperature chart to designate the temperature to which the thermocouple is exposed.

12. The system as dened in claim 8 in which the source of the D.C. signal of reversible polarity comprises a thermocouple and a battery energized potentiometer arranged in opposition, a circuit delivering the unbalance voltage of said potentiometer and thermocouple to said signal winding, a network associated with said last mentioned circuit and including resistors in seriestherein, a feedback circuit between said resistors and the source of reversible D.-C. potential applied to the thyratron grids, resistors and condensers in said network in series in said feedbackcii'cuit, the whole being arranged to provide feedback voltage proportional to the magnitude of the unbalance and proportional to the rate of change of imbalance as represented at said thyratron grids to prevent overtravel and hunting of said motor, a slider on said potentiometer and a mechanical connection between said motor and slider to balance the system for any instantaneous temperature to which the thermocouple is subjected.

13. A motor control system comprising in combination, a two-phase motor having an A.-C. energized winding and a second winding; a pair otthyratrons, a transformer energized from the same alternating current and having a secondary with opposite ends connected respectively'to the anodes of said thyratrons, a midtap on said secondary connected `through said second winding to the cathodes of said thyratrons, means biasing the thyratron grids for partial conductivity at zero grid control voltage; a-source of reversible direct current of variable magnitude connected Vto apply opposite control polarity to said grids and comprising a tube having anode, cathodeV and grid, an impedance, a source of alternating current energizing a circuit comprising said anode, cathode and impedance, meansbiasing said gridfor anode current flow of average value,

asecondtube having an impedance in its anodecathode circuit, said lastmentioned circuittbeingf:

energized inparallel to the first, means adjusting the potential across said second impedance to substantially equal that across the rst at zero grid control potential for the first tube, an output circuit combining said potentials-in opposition for said thyratron grid control; a source of A.-C. grid potential for said first tube of reversible phase and variable magnitude and means responsive to a variable to provide said last mentioned potential representative of the value of said variable.

14. rThe system as claimed in claim 13 in which the source of A.C. grid control potential for the first tube comprises a transmitter having an A.C. energized primary winding and a pair of series connected secondary windings inductively energized from said primary, a magnetic core piece coupling said windings variably in dependence upon the value of a variable, a receiver having a resistor connected in series with the secondaries and a slider, a circuit between said slider and the connection between said secondaries for supplying said A.-C. grid control potential Yand a mechanical connection between the said slider and motor to rebalance the system after a change in the value of the variable.

15. The system as defined in claim 13 in Which the source of A.C. grid control potential for the first tube comprises a primary' and a secondary circuit, a conductor common to said circuits, a coil in each circuit at each of a first and a second location, means magnetically coupling said coils at said locations, a source of alternating current energizing the primary circuit, said grid control potential being developed in the remaining conductor of the secondary circuit, said coupling means comprising a core movable at each location, means to move the core at the rst location in response to changes in a variable and means actuated by said motor to adjust the other core to balance the system after each change in value of said variable.

16. The system as dened in claim 13 in which the frequency of the alternating current for the motor and thyratron power circuits is independent of the frequency of the alternating current used to energize the remainder of the circuit.

17. A motor control system comprising in combination, a variable speed reversible two phase motor having two windings one energized directly from an A.C. source, a pair of thyratrons each having anode, cathode and grid, a trans-.

former energized from said source, and having a secondary with opposite ends connected respectively to the said anodes, a mid tap on said secondary connected .to one end of the other motor winding, a biasing resistor and condenser connected in parallel and between the remaining end of said other Winding and both the said cathodes, said resistor being adjusted to provide partial conductivity for the thyratron at zero grid control voltage, a resistor connecting each grid to the motor Winding end of said biasing resistor-condenser and a source of reversible directcurrent of variable magnitude connected to apply opposite control polarities to said grids at any one time, said condenser having such a capacity as to maintain a conducting bias on the grids under all conditions of cathode load.

ANTHONY J. HORNFECK. HOWARD T. HOFFMAN,

(References 'cn following page) 1' 17 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 18 Name Date Hornfeck Feb. 16, 1943 Ryder Nov. 2, 1943 Jones Aug. 8, 1944 Ryder Nov. 21, 1944 Isbster Mar. 2, 1948 Hornfeck Aug. 17, 1948 Hornfeck Jan. 17, 1950 

